A network of sensors is made up of a plurality of sensors distributed over a geographical area. The function of a sensor is to collect and transmit data relating to a phenomenon that it is desired to study in the geographical area.
It is important to be able to determine the locations of the sensors in the geographical area, firstly for maintenance reasons, and secondly in order to situate where the data has been collected.
Such locating is particularly important when the sensors are movable within the geographical area.
Document US 2009/0128412 describes a method of locating sensors in a network of sensors. For that purpose, each sensor is fitted with a wireless communications module for communicating with the sensors of the network and it includes a distance measuring module.
The distance measuring module is suitable for measuring the distance between the sensor and the other sensors of the network or some of the other sensors of the network. The measured distances are then transmitted to a locating server that determines the absolute locations of the sensors of the network on the basis of the measurements.
That method requires knowledge of the absolute positions of a plurality of sensors, generally of three sensors. Those sensors are referred to as “anchor sensors” and they enable the locating server to determine the absolute positions of the other sensors as a function of the received distance measurements.
By way of example, an anchor sensor may be a fixed sensor of known position or a sensor that includes a module of the global positioning system (GPS) type, or indeed a sensor that includes a position-locating module of some other type and that is suitable for determining the position of the sensor.
For various reasons, it is not always possible to have a sufficient number of anchor sensors for locating the other sensors of the network.
By way of example, these reasons may be installation constraints associated to the site, or indeed problems of energy consumption.
For example, in an application to locating a set of fire-fighters operating at the scene of a fire, with each fire-fighter being fitted with a sensor, all of the sensors are movable. There is no fixed sensor.
Installing position-locating modules on the sensors that are capable of determining their positions and of returning determined coordinates is expensive.
There therefore exists a need for a solution that is simple and inexpensive for locating the positions of sensors in a network of sensors and without requiring the use of anchor sensors.